Space Radar Unearths Secrets of the Ancient Nile

One of the many great mysteries of the Nile River may be solved with the discovery of an ancient river channel buried under layers of sand in the Sahara Desert in Africa.

The buried river channel was revealed in images taken by the Spaceborne Imaging Radar C/X-Band Synthetic Aperture Radar (SIR- C/X-SAR) that flew twice on the Space Shuttle Endeavour in 1994. The radar images were processed at NASA's Jet Propulsion Laboratory and the University of Texas at Dallas (UTD).

"One of the things this discovery helps us examine is the origin of what's called the Great Bend of the Nile," said Dr. Bob Stern, a SIR-C science team member at UTD. "The Nile generally flows due north, but in the Sudan, it makes a huge, looping bend that is really remarkable because the river is flowing through the Sahara Desert, the largest, driest desert on the face of the Earth. There must be a very good reason for the river to make this great bend, otherwise we would expect it to flow straight to the Mediterranean Sea." Instead, it bends southwestward and wanders through the Sahara for another 320 kilometers (200 miles) before resuming its northward course.

"The discovery of the river channel shows us that probably sometime between 10,000 and 1 million years ago, the Nile was forced to abandon its bed and take up a new course to the south. This buried channel proves that this region has been tectonically active and shows us how this activity has forced the river to change its course," Stern said. "Understanding what controls the course of the Nile is a critical part of understanding Nile history and predicting Nile behavior, which is important because the river is essential to millions of people in Egypt, Sudan and Ethiopia."

A scientific paper on the discovery written by Stern and co- authored with UTD geologist Dr. Mohamed Gamal Abdelsalam appears in the Dec. 6 issue of Science magazine. The discovery grew out of research that the scientists have been doing on plate tectonics and the formation of a "supercontinent" more than 600 million years ago.

"Our original experiment involved studying ancient structures in Precambrian rocks that formed where two supercontinents collided hundreds of millions of years ago. In the course of our study, we became interested in how these structures influenced the course of the Nile," explained Stern.

It was the tantalizing radar images of the area hidden beneath the sands of the Sahara that turned the scientists' work in a new direction.

"This discovery wouldn't have happened without SIR-C/X-SAR imagery. Our work in northeast Africa would have been limited to what we could see on the ground or could be seen in satellite photographs. The radar is much more efficient in getting information from these sand-covered areas because the radar waves are able to penetrate the sand. SIR-C/X-SAR imagery has revealed a huge piece of the Earth's surface -- an area that's never been seriously explored before," Stern noted.

"This is one of the most exciting discoveries from the SIR- C/X-SAR mission to date. I expect we'll continue to be surprised by fascinating results like these as the science team continues to analyze the radar data," said Dr. Diane Evans, the SIR-C project scientist at NASA's Jet Propulsion Laboratory. "More and more we are finding the radar data have applications to answer questions about the Earth that were not originally anticipated."

SIR-C/X-SAR is a joint mission of the United States, German and Italian space agencies. The Jet Propulsion Laboratory built and manages the SIR-C portion of the mission for NASA's Office of Mission to Planet Earth, a program to study the Earth's land, oceans, atmosphere and life as a total, integrated system.

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NOTE TO EDITORS: A NASA Television Video File will feature an interview with Dr. Bob Stern and the space radar images on Friday, December 6 at 9 a.m., noon, 3 p.m., 6 p.m. and 9 p.m. Pacific Time. NASA Television is carried on Spacenet 2, transponder 5 (channel 9) at 69 degrees west longitude. The frequency is 3880 MHz. Polarization is horizontal and audio is monaural at 6.8 MHz.